KCNH2 or human ether-a-go-go-related gene 1 (hERG1) encodes the Kv11.1 channel that conducts the rapidly activating delayed rectifier K+ current (IKr) in the heart (Warmke J W and Ganetzky B, Proc Natl Acad Sci USA 91, 3438-3442 (1994); Sanguinetti M C et al, Cell 81, 299-307 (1995); Trudeau M C et al, Science 269, 92-95 (1995); and Zhou Z et al, Biophys J 74, 230-241 (1998); all of which are incorporated by reference herein). Kv11.1 channels are essential for cardiac action potential repolarization and mutations in KCNH2 cause long QT syndrome type 2 (LQT2) (Curran M E et al, Cell 80, 795-803 (1995); incorporated by reference herein). Alternative intronic polyadenylation has been shown to direct the expression of two Kv11.1 C-terminal isoforms, the functional Kv11.1a isoform and the non-functional Kv11.1a-USO isoform (Gong Q et al, J Biol Chem 285, 32233-32241 (2010); incorporated by reference herein). Kv11.1a is produced by splicing from exon 9 to exon 10 and use of a distal poly(A) site in exon 15, whereas Kv11.1a-USO is generated by the activation of a proximal poly(A) site within intron 9. The last 359 amino acids of Kv11.1a are absent in Kv11.1a-USO and the truncated isoform fails to form functional channels when expressed in mammalian cells (Kupersmidt S et al, J Biol Chem 273, 27231-27235 (1998); incorporated by reference herein). A novel LQT2 mutation that disrupted the alternative processing of KCNH2 intron 9 and resulted in switching the expression of Kv11.1 isoforms from Kv11.1a to Kv11.1a-USO was reported (Gong Q et al, Circ Cardiovasc Genet 7, 482-490 (2014); incorporated by reference herein. Thus, the relative expression of Kv11.1a and Kv11.1a-USO isoforms plays an important role in the regulation of Kv11.1 channel function and the pathogenesis of LQT2.
The alternative processing of KCNH2 pre-mRNA is regulated by the relative efficiencies of RNA splicing and polyadenylation events. These events depend on interactions between trans-acting splicing and polyadenylation factors and cis-acting elements present in KCNH2. The poly(A) signal within KCNH2 intron 9 consists of a weak, noncanonical hexamer, AGUAAA (Gong et al, 2010 supra). When this poly(A) signal is changed to the strong, canonical poly(A) signal, AAUAAA, polyadenylation becomes the dominant reaction, resulting in the predominant expression of Kv11.1a-USO. The elimination of the intron 9 poly(A) signal by the AGUAAA to CGCAAA mutations results in predominant expression of Kv11.1a and an increase in channel current.